I used to work the wash rack as a hostler helper, and SP washed engines at Taylor until around 1974 or so, when there was a drought, and used that as an excuse to stop...cut jobs and you began to notice just how grey, grey could become. I have weathered several models of early 1970's diesels to fully reflect this fine period of SP cleanliness......

When some engines were so bleak that you couldn't work on them for the dirt, they had a "wash rack" off of the turntable by the paint spray enclosure, and you'd see these guy with high pressure steam cleaners peeling off the burned oil. Some of them got so bad like that, you couldn't repaint them without doing that inside and out first.

We had an oil testing program for a while way back then, with engines painted with stencils of "test oil" do not change.....and we had at least one wag, if not more, somewhere on the SP system, who used to wipe the grime to say: "test dirt, do not remove"........and these often stayed that way for years.....

They wash engines when they need to and not one bit more, it's a piece of heavy equipment, it doesn't have to look pretty, and it costs time and money to wash them. Amtrak and the Commutes wash more because they want to look pretty for their customers.

The reg's excuse sounds more like an urban legend, since they've been blowing off washing engines since about the 1970's.... Although all large water users, like car washes, and industrial users, RR's included, are subject to more wastewater recovery and discharge cleanliness regs. and actual scrutiny today, than back in the "bad old days" when folks dumped some pretty wicked crap back into the water table without anyone even knowing any better.